In the 1960's it was realized that many elective tonsillectomies were probably unnecessary and the number performed in the United States decreased dramatically - from 1,400,000 in 1959 to 400,000 in 1979. However, adenotonsillectomy remains once of the most common surgical procedures performed on children, and is responsible for significant health care expenditures (over 800 million dollars annually in the U.S.). Today, many of the indications for adenotonsillectomy are still poorly defined and controversial, and significant variation exists in the rate of adenotonsillectomy performed in different geographic regions. Some conditions, such as sleep apnea, appear to improve after adenotonsillectomy whereas others, such as recurrent infection, may show only short-term benefit compared with watchful waiting or medical therapy. No studies have evaluated the impact of tonsil and adenoid (T and A) disease on the health status or quality of life (QOL) of affected children. Before prospective clinical trials can be carried out to compare the appropriateness and effectiveness of surgical and medical treatment, we need to objectively measure the disease-specific health status of affected children. In addition, further research is needed to define the natural history of T and A disease. Therefore, the goal of this research is to create a valid, reliable, sensitive, and comprehensive disease-specific health status instrument for use in health services research on pediatric T and A disease. As in other pediatric health status instruments, the T and A instrument will be completed by the parent of the affected child. We propose a prospective instrument validation study in three phases. Phase 1 (focus groups, item development, initial item testing and reduction, and development of a beta-version) has already been completed as a pilot study. In phase 2, we will assess the test-retest and internal consistency reliability, construct and criterion validity, and between-groups discrimination of the beta-version of the instrument - using existing generic instruments, objective clinical measures, and a control group of patients without T and A disease. Phase 3 of this study will assess the sensitivity of the instrument to change in clinical status. We anticipate that validation of the T and A instrument will be completed in 24 months.